The invention relates to a dielectric resonator demultiplexer having a particular, but not necessarily an exclusive, application for communications satellite payloads.
Satellite communication systems are used for a number of different purposes, for example, ground surveillance, and telecommunications. The cost of placing communications satellite payloads into orbit is very high and it is desirable to have compact, reliable and light weight resonator filter structures that are sufficiently rugged and stable to withstand both the high levels of vibration experienced by space hardware during the launch phase of a mission and also long term effects of repeated thermal cycling experienced ever the duration of the mission. It is of importance to ensure in communication satellite payloads that a stable performance is maintained over a wide range of temperatures.
With known demultiplexer arrangements for communication satellite payloads, the resonant filters of the demultiplexer are mounted on the payload such that the longitudinal axes thereof are substantially parallel to the payload mounting surface.
With these arrangements, the area occupied by the demultiplexer, i.e. its "footprint", is fairly large and the mounting arrangement for the filters must be such that each of the resonator elements of the filters is not subject to undue mechanical and/or thermal stress.
The resonator cavity walls of the known arrangements are relatively thin and thereby susceptible to Induced mechanical/thermal stressing caused, in the main, by the mounting arrangements.
It is usual for the mounting arrangement to be in the form of a composite base plate i.e. a carbon fiber base plate, which is relatively light, but extremely expensive. The composite base plate has a low coefficient of thermal expansion and thereby minimizes thermal stressing of the filters.
In order to minimize the transmission of mechanical stresses from the composite base plate to the filter, it is necessary to interpose shims, i.e. extremely thin washers, at each of the points where the base plate is mounted on the payload mounting surface. The correct shimming arrangement is difficult to achieve but, once in place, is effective to reduce mechanical stresses.